Articles from Lapidary Digest
FINDING AND FINISHING AMMONITES
Edmonton, Alberta, Canada
Copyright 1997-1998. This document may be copied and used in
mineral and gem club newsletters without asking permission, given
that the article is reprinted in toto and that cedit is given the
author and Lapidary Digest as the source. Others wishing to reprint
the article may send a rquest to Lapidary Digest, using the e-mail
form on the first page.
Somewhere in the Lower Middle Devonian, some group of Nautiloids gave
rise to a modest group of coiled Cephalopods, the Ammonites. They really
picked up their pace in the Mesozoic Period and became more plentiful
and varied, and were dispersed almost worldwide. They differed somewhat
from their modern day cousins, mainly by internal structure.
As they died on the ocean floor, they were buried in the sea mud. In
North America that mud became, for the purpose of this paper, either
shale or Ironstone. Normally the mud would be pressed into flat layers
of shale by the pressure of sea and mud above it, but the hard bodies
kept their shape and became concretions. Those concretions, or roundish
UFO shaped nodules of shale and Ironstone, are found in the Aragonite
Zones of the Badlands, in Southern Saskatchewan, Southern and Mid Alberta,
and Northern Montana and are the geologic structures where Ammonites
are found today. You usually find the concretions in the upper sides
of banks on existing rivers, such as the Bow River, or in the Badlands
banks, which were rivers at one time. Surface collecting is easiest,
although some rockhounds have adapted a type of long tined pitchfork
for prodding down into the soft Bentonite beds in hope of striking a
Once found, the trick is to break open the concretion. If cleaned off
carefully, one can usually see small fracture lines or, sometimes, a
piece of the Ammonite peeking through a spot at the edge of the nodule.
A sharp chisel, a hammer, and a steady hand, and most concretions will
break in half where the Ammonite is laying usually exposing a concave
side of the concretion with shell attached and the Ammonite itself imbedded
in the other half. If you are after the Gem...or shell....then you can
break the Ammonite out of the now halved concretion. But, if you want
a complete Ammonite, if indeed it is complete, then traditional methods
of removing a fossil from matrix are used. Thank goodness for Foredoms
and Dremels :)
Trivia time...The Ammonites got their name from the chief God of the
Triad of Thebes Amun, who was often depicted as a Ram with curved horns.
The area covered by the Bearspaw Sea, which included Northern Montana,
Alberta and Western Saskatchewan is where we find most of the Placenticeras
Meeki species. The Meeki is, in my humble opinion, the best gem quality
shell. These concretions with, hopefully, Meeki inside of them, can be
anywhere from 6" to 3' in diameter! The bigger ones, and most others,
are "halved" right there on the spot to see what treasures they hold
and to more easily get them back to your transport. Most will fit into
a backpack but some we have to "sling" and carry these on our backs also.
Heavy?......You Bet !
But alas, sometimes you find the other kind, what we call barren shale,
and your efforts of digging them out and breaking them in half are not
Hmmm, heavy....reminds me of a time when I was loaded down with a heavy
pack full of Ammonite, walking on a game trail at the bottom of a coulee
on the way back to my truck. I came around a corner, with my head down..of
course, (typical Rockhounding syndrome) and came face to face with a
huge Whitetail Buck! Now, it's nice to see nature from a distance, but
up close those bucks are huge!!! He startled me and I fell backwards
on my pack and watched as the buck took off straight up the side of the
coulee like the hounds of hell were chasing it. I recall, as I laid there
looking up, that the bank was about 100 feet high and pretty well straight
up! Well, after kicking my legs for a while, and laughing at my predicament
of looking, for all the world, just like a Turtle flipped on it's back
with it's legs wiggling, and rocking my body I finally rolled on my side
and managed to get back to my feet. To this day, I still don't know which
one of us were scared more, the Buck or me. :)
Do you still want to go hunting for these concretions with that beautiful
Ammonite shell inside? A word of warning, you must, at least in Canada,
have the appropriate Ammonite permit to collect Ammonites! The fine can
be severe for collecting without one. But it doesn't stop with a license;
once you have returned home with your collected treasures, you must then
fill out a disposition form and take pictures of your finds, which are
sent off to the Tyrell Museum, where the experts look things over. If
you have not discovered a new species or anything of paleontological
value, they send you a reply...and then the Ammonites are yours.
...FROM RAW TO GEM AMMONITE
I will attempt, in my humble way, to describe to you the way in which
I work my Ammonite. Please bear with me, as writing is not my forteí.
Once I have gotten my Ammonites home, itís time to clean them and see
what Iíve got. This can involve anything from Muriatic acid baths ..
.remember AAA, Always Add Acid ... never add water to acid, to a simple
cleaning with a brush and water. Some Ammonite has a thin film of white,
or unformed, Calcite on top of the gem, this is when Acid is used in
dilute amounts to clean it off. If itís too filmy it usually extends
down through the shell and makes it rather useless for Gem Quality pieces.
Although with acid, the colors are still there.
Next comes the decision to keep it whole..if indeed you found a whole
one in one piece, you should keep it as such.....or to "gem it", if itís
in many fractured pieces. If itís whole, itís sanded by hand later. Iíve
found no better way to do it, although Iíve experimented plenty.
Ammonites, it seems, always start their lives with dark colored, blue
or green, shells. Probably to aid them in hiding from their many predators.
Their shell is in layers, starting from red, to the oranges and yellows
and then to the greens and blues of the last layers. So, if you feel
brave, you can continue to sand down through the layers to get at the
rare greens and blues. But, like an opal, be careful, after the last
blue color...thereís nothing but shale and you will have lost your color!
But alas, I wander off...... Back to it then.:) There is much to do before
laying on the sandpaper. Firstly, if not whole, you must cut away the
excess shale, this can be a tricky process also. You should try and keep
about Ĺ " of shale still attached to the Ammonite Gem. Remember, the
Ammonite is a Nautiliod and shaped accordingly, albeit flattened out
somewhat from the pressures of time. Therefore there will be gem on "both
sides" of the Ammonite, and you have to decide where to cut it. Flat
spots are preferred, but they are rare in a Nautiloid shaped body.
Depending upon the color of the shale you probably have to seal the Ammonite.
If whole, then you seal the whole Ammonite. But for this paper, letís
assume that you have Ammonite pieces. The reason for sealing the Ammonite
is to darken the shale down and to seal the gem shell to the shale beneath
it. Again, referring to opal, the darker the matrix, such as Black Mintabe
Opal, the brighter the color or fire is seen. Same thing with Ammonite
gem. The darker the shale below, the brighter the colors of the gem will
seem to be.
Sometimes, Ammonites come with the shell sitting loosely on the shale
cores. This is where the Opticon Sealer comes in. You need to heat the
Ammonite pieces up to about 150 degrees and the apply the sealer to the
gem with a brush. I use sheets of Ĺ inch steel and lay them across the
burner elements of a kitchen range. But if youíre doing a single piece,
or just a few, a slow oven will do just nicely. The warm stone will actually
draw the sealer down through the gem and into the shale beneath it, thus
effectively sealing the
gem to the shale and making the shale darker. Take the pieces off the
heat and let them sit for a few days. The sealer never quite seems to
harden, but almost.
Now, the pieces have to be cut into your fairly flat pieces or freeforms.
Not too small yet as you have to use the Lap wheels next. I guess this
part just takes practice, but you can actually find some fairly flat
pieces on the Ammonite .... you just have to picture flat enough places
and sizes to eventually make gems from. Sometimes your pieces are small.
But they are flat! :)
The Gem Quality of the pieces are important and could alter your decision
for gem or freeform pieces. "A" grade or better have a finely fractured
texture with either a multitude of colors or a single brilliant color.
The grades differ to c,b, a,aa,and triple a grades. Now that we have
formed the AFAC we hope that the grades can be regulated. But for now
beware, some peoples ideas of A grade are not always the same as someone
elses. Some gem has wide fracture lines and poorer colors and are therefore
of lesser quality. After you done it for a while, you can tell this when
you first crack open the concretion.
Next comes the flat laps. I usually start with about a 400 grit ...carefully
...the gem is not that hard. Think of it as a regular shell and youíll
be fine. All you want to do in this stage is to "flatten" the piece you
are working on. Some of it, of course, can never be flattened and I believe
these pieces would be great for intarsia work, but since I havenít got
that figured out yet, for freeform pieces. Once you have your piece fairly
flat, look at the center of the piece, youíll probably find...if you
stopped soon enough .. that itís the green or blue color. If you didnít
stop soon enough, then youíll find shale,...Damn! And you start over
with a flatter piece. :) Seriously though, keep an eye on it and youíll
be fine. This is the stage where you must decide, freeform or gem quality.
If you are doing gems instead of freeform, you cut out your gems before
you start your 600 stage. The most popular way to cut the gems .... which
also gives you the least waste...is the rock bandsaw. But, the traditional
saw is fine, just plan your gems out carefully as to waste as little
of it as possible.....itís expensive stuff!! An oval of 10x14 can be
$80.00 or more if itís of "AA" or better!
I dop my gems with a two part 5 min epoxy on to welding rod pieces. Just
warm up the metal rods with a torch slightly and stick it to the already
placed epoxy on the back of the gem (the shale). I round them into calibrated
shapes with a 400 or 600 grit expandable wheel with sc grit.
Finally, the gem must be capped. Some Lappers use glass, some use a product
such as Envirotex .. a two part sealer/glue that hardens rock solid.
These methods are ok, but for rings and high abuse jewellery you still
canít beat Spinel or Quartz Caps. I use tempered glass or I make my own
caps from Quartz, for Brooches and most of my freeforms.
I hope I have been able to shed some light on the long kept secrets of
Ammonite Gems. But if we are going to sell rough, people need to know
how to work it properly. Itís too precious and beautiful a gem for people
to have to learn the hard way, as I did.